The present invention is related generally to the production of a smooth, clean surface for receiving a data bearing film or coating used in conjunction with the manufacture of machine readable data storage or recording devices such as compact discs and the like.
The proliferation of digitally recorded data of many types, including information, audio and video signals has created a substantial industry in the production of data recording and storage devices including those commonly known as compact discs or CDs, video discs, CD ROMs and other devices. Typically, these data storage discs are manufactured of a polymer material which is molded by a metal master device, commonly known as xe2x80x9cstamperxe2x80x9d, to create machine readable digital data logic surfaces on data storage discs such as compact discs.
The stamper is a metal part which forms a part of an injection mold. The stamper carries complement logic surface portions (either pits or bumps) and is inserted into the mold cavity to become one side of the cavity. The stamper is electro-formed from a xe2x80x9cmotherxe2x80x9d, which is a metal part electroformed from a xe2x80x9cfatherxe2x80x9d. The father is the first electroformed metal part made from a xe2x80x9cglass masterxe2x80x9d. The glass master is a medium on which data is recorded as the first step leading to the replication process. The glass master is of a glass disc larger than the replicated product disc, and is coated with a photosensitive material on which the data are recorded by a laser beam recorder. The replicated product discs, for example compact discs or video discs, are replicated from the stamper.
The creation of the metal master (father) and its replications requires careful attention. For example, data recording or storage devices or compact discs (CDs) are usually optically read to transfer the stored data to a machine which is capable of manipulating the resultant signals for one purpose or another. The minute surfaces which are generated on the data storage xe2x80x9cCDxe2x80x9d must be produced to very close dimensional tolerances in order to effect accurate transfer of the signal or stored data to the reading device which typically utilizes a reflectable light or laser beam. Accordingly, careful attention is paid to the production of the metal master (father) which is used to produce the data storage discs. This careful attention has resulted in the development of fairly complex processes for producing the master discs or devices to be sure that there are no surface imperfections which could result in the production of erroneous data or information on the production copies of the data storage discs. There have been continuing problems and inefficiencies in the manufacture of master discs which are substantially overcome by the present invention.
Common practice in the production of master discs for producing CDs or similar data storage devices includes the use of a glass, plastic or metal plate, generally of larger diameter than the xe2x80x9cend productxe2x80x9d data storage disc and which serves as a substrate or support member for a thin data bearing film or coating. This film is then treated to provide surface geometries, either pits or bumps, which are replicated in the metal master disc (stamper) described above. Although the glass, plastic or metal substrate member is often referred to as a xe2x80x9cmasterxe2x80x9d, it is actually a supporting substrate for the data bearing film which is used to create the metal master disc that is used in molding the production data storage or recording discs.
A substantial problem in the application of data bearing films is that of maintaining the surface quality and cleanliness of the substrate member. The film support surface of the substrate member must be flat in the area where data will be recorded and, particularly smooth and void of any surface roughness or imperfections. For example, the data bearing film that will be applied to the substrate surface is generally about 1500 to 1600 Angstroms in thickness. Tiny logic xe2x80x9cpitsxe2x80x9d or xe2x80x9cbumpsxe2x80x9d are then produced on the data bearing film and are typically sub-micron in width. Consequently, even a small scratch or particle disposed on the surface of the substrate member can destroy a large area or several tracks of data. It is not difficult to damage or scratch the substrate surface or contaminate the surface to provide a roughness of five microns or more. The human eye cannot detect a five micron particle or surface imperfection.
Accordingly, the production of the substrate member for supporting the data bearing film is expensive and favors the cleaning and recycling of the substrate members in the interest of economics in the production of data storage or recording devices. The original acquisition cost of glass substrate members requires that they be reused until the surface condition is completely unacceptable. Of course, the recycling process must cost less than the original cost of the substrate member itself. The average yield in producing so-called master discs by current methods using a glass substrate member and a data bearing film applied thereto is generally less than 90% and may be substantially less if production demand is high for the end product data storage disc. The yield may vary from day to day according to personnel variances and environmental changes.
Another problem associated with the use of the above-mentioned substrate members is that the commonly used data bearing films or coatings have poor adhesion characteristics to the substrate member support surface. This requires that an adhesion layer be applied to glass substrate surfaces, in particular, before the data bearing film is applied. The adhesion promotion material is generally spin-coated onto the substrate member. Hexamethyldisilane (HMDS) is a commonly used adhesion promoting material for data bearing films. It is an expensive chemical, difficult to apply and to remove when recycling the substrate member and a waste disposal problem. Moreover, the process of applying the adhesion promoting layer to a substrate member also increases the risk of contamination of the substrate surface with particles that can damage the surfaces of the data bearing film.
Notwithstanding the problems of contaminating the surface of the substrate member with a film adhesion promotion material, the substrate member, during its reclamation process, is typically soaked in hot nitric acid, cleaned by ultrasonically activated detergents, rinsed multiple times in a solution of alcohol and deionized water, and often a final rinse in alcohol together with drying by hot fluorocarbon gasses. Moreover, if a surface has been damaged in any way it must be mechanically repolished and recleaned. Clearly, the facilities and material requirements for processing or recycling these data bearing film substrate members are significant and require careful attention to employee training, handling of volatile and toxic fluids, and is a significant cost factor in the production of digital data storage or recording devices.
The present invention provides improved methods and means used in connection with the production of data bearing films, including those films used to manufacture master discs and similar devices for the production of data storage and recording devices, including those commonly known as compact discs or CDs, CD ROMs and laser video discs.
In accordance with one aspect of the present invention, a method for preparing a substrate for receiving a data bearing film has been developed wherein a substrate member is coated with a layer of a hardenable resin which provides a flat, smooth, substantially defect free surface and to which a data bearing film or coating may be directly applied without contamination or the development of surface imperfections on the data bearing film.
In accordance with another aspect of the invention, a method has been developed for preparing data bearing films for receiving a layer of metal to produce the father disc from which the mother and stamper (children) discs are electroformed for data storage disc manufacturing processes wherein a master substrate member is provided which may be coated with a layer of material which will fill surface imperfections in the substrate member, and encapsulate particulates and other contaminants on the substrate surface so that they cannot interfere with the data bearing film layer and which enables the master substrate member to be reused with substantially reduced reclamation and preparation costs.
In accordance with yet a further aspect of the present invention, a method is provided for conditioning a substrate member for receiving a data bearing film or coating wherein minimal exposure to contaminants is obtained, where the overall process of preparing the data bearing film and manufacturing the master disc is simplified and may be carried out in a clean environment. Accordingly, the overall cost for producing high quality masters for the production of data recording and storage elements or CDs is substantially reduced.
The present invention still further provides an improved substrate member for receiving a data bearing film which is substantially free of surface imperfections, may be conveniently reused with minimal recycling or reprocessing costs, and is adapted to provide for an improved method of manufacturing so-called master discs for generating production data recording and storage devices.
Those skilled in the art will appreciate the above-mentioned advantages and superior features of the invention together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawings.